1. Field of the Invention
The present invention relates to a method for manufacturing an overrunning clutch that is used in an engine starting apparatus, etc., for example.
2. Description of the Related Art
In conventional methods for manufacturing overrunning clutches, in apparatuses that include: a tubular driving body that has a plurality of tapered notches formed circumferentially on an inner circumferential portion; a transmitting body that has a first end portion that is inserted into the inner circumferential portion of the driving body so as to form wedge-shaped spaces between an outside diameter portion of the first end portion and the notch portions; and rollers that are mounted into the wedge-shaped spaces so as to be movable in a circumferential direction, and in which a driving force is transmitted from the driving body through the rollers to the transmitting body by unidirectional rotation, upper limits of unidirectionally transmitted torque have been suppressed to predetermined values by disposing stopping portions that project inward at the narrow ends of the wedge-shaped spaces on the inner circumferential portion of the driving body at uniform positions in a circumferential direction such that the rollers come into contact with the stopping portions at positions where they bite into narrow portions of the wedge-shaped spaces, and restricting the amount of bite of the rollers at the contact positions so as to be at a required amount when the diameter of the outside diameter portion of the first end portion of the transmitting body, which is made larger as a preventive measure, becomes smaller (see Patent Literature 1, for example).
Specifically, a driving body that has predetermined dimensions is prepared by preparing a driving body in which a plurality of tapered notches are formed by cold forging, forming portions that cannot be formed precisely by cold forging, such as end surfaces, etc., by machining, and subsequently applying heat treatment in order to ensure mechanical strength. Similarly, a transmitting body that has predetermined dimensions is prepared by preparing a transmitting body by cold forging, forming portions that cannot be formed precisely by cold forging, such as end surfaces, etc., by machining, and subsequently applying heat treatment in order to ensure mechanical strength. Here, the outside diameter of the first end portion of the transmitting body that is to be inserted into the inner circumferential portion of the driving body is formed so as to be enlarged. Then, the outside diameter of the first end portion of the transmitting body is finished such that the upper limit of the transmitted torque is at a predetermined value.
Next, an overrunning clutch is produced by combining a driving body, a transmitting body, rollers, springs, etc., that are each prepared so as to have predetermined dimensions.    Patent Literature 1: Japanese Patent Publication No. HEI 7-113383 (Gazette)
In conventional methods for manufacturing overrunning clutches, the upper limit of the transmitted torque depends on the amount of bite when the rollers come into contact with the stopping portions that are disposed on the driving body. Because the overrunning clutch is produced by combining parts such as the driving body, the transmitting body, the rollers, etc., that have been prepared separately, one disadvantage has been that the upper limit of the transmitted torque becomes irregular due to irregularities in the inside radii of the notch portions, irregularities in the positions where the stopping portions are formed, irregularities of the outside diameters of the rollers, and irregularities in the outside diameter of the first end portion of the transmitting body, etc.
In addition, if an attempt is made to ensure a minimum required transmitted torque with consideration for irregularities in each of the parts, target values for each of the parts must be set somewhat higher, inevitably also making the upper limit of irregularities in each of the parts higher. Even in that case, size must be increased in order to prevent damage, giving rise to increases in the size and weight of the machinery. It is difficult to raise precision, particularly in the driving body, since heat treatment is applied after cold forging, giving rise to quench warping.
It is also conceivable for irregularities in the upper limit of the transmitted torque to be suppressed by measuring the inner circumferential shape of the driving body and selecting and combining the rollers or the transmitting body based on the results of that measurement. However, because the inner circumferential shape of the driving body is complex, the inner circumferential shape of the driving body must be measured by a three-dimensional measuring instrument, requiring a lot of measuring time. In addition, since the amount of bite of the rollers at the contact positions is found using complex formulae based on such measured values, it has been difficult to calculate the amount of bite with high precision.